Simulation and optimization of the waste heat recovery system of the ship power system based on the heat current method

Abstract

AbstractWaste heat recovery technique is of great importance to improve the coefficient and reduce the emission of greenhouse gas for ship power system. This paper builds the model of a waste heat recovery system of single pressure Rankine cycle with heat current method. Combining with the thermo‐electrical analogy method, the global heat current model of waste heat recovery system is obtained, which indicates the direction of heat flow, the distribution of thermal resistance and the relationship of temperatures. Applying the law of Kirchhoff builds a mathematical model of a system with no intermediate nodes temperatures. Considering the variation of physical property and distribution of thermal resistance in phase change heat exchanger, a double nested iteration solving algorithm is proposed. The results show that the heat transfer rates of economizer, superheater evaporator, condenser, and steam receivers are 9.1, 70.42, 143.89, 19.03, 171.98, and 17.28 kW, respectively. With the objective of maximum output of turbine, applying the genetic algorithm obtains the optimal mass flow rate of cycle water, which is 0.53 kg/s and improves the output of turbine from 53.25 to 147.45 kW. Discussions on the optimization model show that decreasing extraction ratio and increasing the mass flow rates of air discharge of compressor will increase the output work of turbine. Both the optimal mass flow rate of cycle water and maximum output work decrease rapidly at first and then change little while the circulation ratio increases. Particularly, the relative variations of mass flow rate and output work are less than 2% while the circulation ratio is larger than 4.